1. Field of the Invention
The invention relates to an assembly including a holder--in particular, a mount--and a transparent, preferably optical, component that transmits in the ultraviolet spectral region, and more particularly to an assembly in which an adhesive can be hardened by means of UV light within a given spectral distribution.
2. Discussion of Relevant Art
Japanese Patent document 8-72300 provides an example of such an assembly with an ultraviolet curable adhesive. Such assemblies form, among other things, mounted lenses and the like of illumination systems and projection systems for microlithography.
Adhesive bonding to a mount is known, for example, for automobile and architectural glass, wherein the adhesive is protected from the effects of solar UV irradiation by means of UV-absorbing fillers and protective layers.
Thin layers of dielectrics, and in protective layers with thicknesses in the micrometer range, are known in the optical field, and are applied by vacuum deposition, sputtering, PVD or CVD. Such a protective layer for UV hardening bonds is described in Japanese Patent publication 9-184917.
According to Naumann, Schroder, Constructional Elements of Optics, Munich and Vienna 1983, page 72, such layers of cryolite, magnesium fluoride, cerium fluoride, zinc sulfide and titanium dioxide have lower transmission limits of 0.12 to 0.4 .mu.m. Tantalum pentoxide, hafnium dioxide and mixtures of them transmit from 0.3 .mu.m or 0.32 .mu.m, according to Soviet Patent Document SU 48 23 642/33.
In general, the exact reflection, absorption, and transmission spectra of these thin layers in the Deep Ultraviolet (DUV) region are not known, since the effects of the substrate and of the spectrometer/monochromator components are difficult to detect, and these materials have not been tested outside the planned field of application.
It has been found that the known mount adhesives based on epoxy resin, which can be hardened with UV light of the Hg-I line, can be considerably damaged by irradiation with DUV light at 248 nm and even more at 193 nm, in DUV projection exposure equipment, and by their failure limit the life of the equipment.
DUV absorbing fillers in the adhesive mass do not prevent failure of the boundary layer of the adhesive adjacent to the quartz glass.